Jun 10, 2015 - Recorder: Agilent. DSA-X 93204A, bandwidth 33 GHz, sampling interval 12.5 ps. FIG. 4. Simulated evolution of the electric field strength Er at ...
Suppression of shunting current in a magnetically insulated coaxial vacuum diode M. I. Yalandin, G. A. Mesyats, V. V. Rostov, K. A. Sharypov, V. G. Shpak, S. A. Shunailov, and M. R. Ulmaskulov Citation: Applied Physics Letters 106, 233504 (2015); doi: 10.1063/1.4922484 View online: http://dx.doi.org/10.1063/1.4922484 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/106/23?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Preliminary investigation of an improved metal-dielectric cathode for magnetically insulated transmission line oscillator Rev. Sci. Instrum. 86, 024705 (2015); 10.1063/1.4907934 Suppression of the asymmetric competition mode in the relativistic Ku-band coaxial transit-time oscillator Phys. Plasmas 21, 103108 (2014); 10.1063/1.4900408 Electrical strength of multilayer vacuum insulators Appl. Phys. Lett. 93, 241502 (2008); 10.1063/1.3054344 Repetition rate operation of an improved magnetically insulated transmission line oscillator Phys. Plasmas 15, 083102 (2008); 10.1063/1.2965143 Vacuum insulator development for the dielectric wall accelerator J. Appl. Phys. 104, 023301 (2008); 10.1063/1.2956702
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APPLIED PHYSICS LETTERS 106, 233504 (2015)
Suppression of shunting current in a magnetically insulated coaxial vacuum diode M. I. Yalandin,1 G. A. Mesyats,2 V. V. Rostov,3 K. A. Sharypov,1 V. G. Shpak,1 S. A. Shunailov,1 and M. R. Ulmaskulov1 1
Institute of Electrophysics UD RAS, Ekaterinburg 620016, Russia P.N. Lebedev Physical Institute RAS, Moscow 119991, Russia 3 Institute of High Current Electronics SD RAS, Tomsk 634055, Russia 2
(Received 6 March 2015; accepted 31 May 2015; published online 9 June 2015) Real-time investigations of the dynamics of explosive electron emission from a high-voltage cathode holder made of nonmagnetic stainless steel in a magnetically insulated coaxial vacuum diode have been performed. It has been shown that aging the cathode with several tens of voltage pulses at a field of 1–2 MV/cm provides a stray emission delay ranging from hundreds of picoseconds to a nanosecond or more. In addition, the magnetic field must be configured so that the magnetic lines would not cross the vacuum gap between the diode case and the cathode holder in the region behind the emitting edge of the cathode. These efforts provide conditions for stable emission of the workC 2015 AIP Publishing LLC. ing beam from a graphite cathode with a sharp emitting edge. V [http://dx.doi.org/10.1063/1.4922484]
To produce high-current electron beams in relativistic high-power microwave (HPM) oscillators, magnetically insulated coaxial diodes (MICDs, Fig. 1) with a sharp-edged cathodes made of pyrolytic graphite are widely used (see, e.g., Refs. 1 and 2, and citation therein). Graphite is preferable material due to specific morphology of the surface containing numerous micro-protrusions, i.e., elementary electrons’ emitters. Increasing microwave frequency3 with microwave power kept unchanged4 decreases the MICD dimensions proportional to the wavelength, increases the electric field strength (E) at the cathode electrode in reverse proportion to the MICD dimensions, and, as a consequence, increases the probability of electron emission from any section of the overvolted coaxial vacuum transmission line (VTL, Fig. 1(a)) formed by a segment of the MICD case and the cathode holder. Therefore, a backward (stray) electron current may arise in the MICD. In subgigawatt relativistic Ka-band backward wave oscillators (BWOs),5–8 the radial electric field in the VTL can reach 1 MV/cm (hereinafter, we imply the macroscopic E field). In this case, the sputtering of the cathode, operating in the mode of explosive electron emission (EEE), makes special treatment (prepolishing) of the VTL electrode and use of a vacuum better than 103–104 Torr inefficient. Thus, the stray emission in the VTL cannot be completely eliminated, but one can attempt to prevent it during the delay time to the onset of EEE.9–11 The appearance of a backward current that shunts the useful (forward) e-beam is especially critical in cases where the beam is used for in-phase excitation of several HPM oscillators.12–15 Anyway, this current must be completely absent in the range
